The operational efficiency and the overall power output of a gas turbine engine generally increases as the temperature of the hot combustion gas stream increased. High combustion gas stream temperatures, however, may produce higher levels of nitrogen oxides (NOx). Such emissions may be subject to both federal and state regulations in the U.S. and also may be subject to similar regulations abroad. A balancing act thus exists between the benefits of operating the gas turbine engine in an efficient high temperature range while also ensuring that the output of nitrogen oxides and other types of regulated emissions remain well below mandated levels. Moreover, varying load levels, varying ambient conditions, and other types of operational parameters also may have a significant impact on overall gas turbine efficiency and emissions.
Several types of known gas turbine engine designs, such as those using Dry Low NOx (“DLN”) combustors, generally premix the flow of fuel and the flow of air upstream of a reaction or a combustion zone so as to reduce NOx emissions via a number of premixing fuel nozzles. Such premixing tends to reduce peak flame temperatures and, hence, NOx emissions.
For fuel flexibility and power system availability, low emissions gas turbines are often equipped with a system to inject a liquid fuel as a secondary or a backup fuel in addition to the gas premixers. The liquid fuel injectors may be inserted through the center of the gas premixers. Because the liquid fuel may not evaporate and premix sufficiently with the air prior to combustion, large quantities of water may be injected into the combustion zone so as to reduce the flame temperatures and the resultant NOx emissions. A significant and expensive volume of water thus may be required when operating with such a liquid fuel. Moreover, water injection may lower overall gas turbine efficiency.
There is thus a desire for an improved dual fuel premixing nozzle. Such a premixing nozzle may accommodate a secondary fuel such as a liquid fuel with reduced overall water consumption while maintaining gas turbine thermal efficiency and power generation.